Sprayable coatings are extensively used in many industries. Coatings may be metallic or non-metallic, organic or inorganic, and are available in powder, solution, suspension, or colloidal form for application by plasma, electrically or non-electrically-charged spraying systems.
Sprayable coatings are applied to a workpiece for a multitude of purposes. Among the more prevalent purposes are the establishment of thermal, chemical or wear protection barriers, to meet section thickness requirements necessary for structural strength or rigidity, for improvements in flow patterns around or through the coated workpiece, or to enhance or to block electrical conductivity.
Sprayable coatings may be applied to a workpiece with the aid of process control. Process control, which may be provided by CNC instrumentation, simultaneously controls a number of operating parameters. An important operating parameter is flowrate of the spraycoating material through the spray unit. Another important operating parameter is control of the host carrier, i.e. the hardware to which the spray unit is attached. In general, the host carrier must provide several degrees of freedom of motion necessary for precise positioning of the spray unit (and its ancillary equipment) in relation to a workpiece.
A significant problem associated with the deposition of sprayable coatings is the determination and control of the optimum sprayhead distance from the workpiece. Precise control of this parameter is critical for the achievement of the required coating. A workpiece with simple or planar surfaces is easily measurable for sprayhead positioning using relatively simple mechanical measurement techniques. However, as workpiece surfaces become more complex in shape, measurement of distance by these techniques becomes difficult or even impossible. These more complex target surfaces range from intricate curves and bends to inner diameters and complex internal structural members and recesses.
Another problem is determining the optimum sprayhead path in relation to the workpiece. Control of the sprayhead's path as it traverses the workpiece is critical for achievement of proper coating thicknesses. Ideally, proper spraycoating thicknesses can be accomplished by controlling the sprayhead's motion as it traverses the workpiece on a per unit time basis or by control of the sprayhead's peripheral overspray pattern. This is especially important in the creation of tapered coatings which range from full-depth to a flash.
The current art attempts to determine proper spray coating depths and coverage through the use of cumbersome mechanical standards. Depths are manually gauged with mechanical probes, from which the distances from the sprayhead to the target surfaces are manually calculated. These data are then inputted to a numerical controller.
Several serious problems exist with this approach. First, mechanical probes cannot always reach the deepest or most convoluted recesses of a highly engineered workpiece. Inability to properly calculate the depth of a given recess results in improper spray coverage and coating thickness. Second, the related art does not provide for calculation of the sprayhead's angle of spray delivery when the sprayhead traverses a non-planar section of the workpiece. This results in variable coating thicknesses and uncontrolled overspray.
Third, the current art does not provide the operator with the means to visually confirm the new program for a given workpiece. Fourth, the current art's method of programming is not only imprecise, but is very time-consuming to establish. Current practice requires extensive set-up time of the initial workpiece, which reduces the availability of production equipment for other revenue-generating purposes.
Fifth, several reworking operations are considered the norm in correcting the inevitable defects which occur due to inaccuracies in the current art. These defects include over- and underspraying of the workpiece, with related improper coating thicknesses. Expenses related to these reworking operations, such as scrapped material, related additional labor, and increased scheduling demands of production equipment, are necessarily related to higher production costs, and ultimately, to higher costs to the consumer.